1. Field of the Invention
The present invention relates to container materials having a deoxidation function which can remove oxygen present in sealed containers to prevent changes in quality and properties of food and drink contained in cans and sealed containers, etc. and enable their long term storage, and also relates to a method of removing oxygen in the sealed containers prepared using such materials. The term "sealed container" used in the present invention means all kinds of sealed containers, such as cans, bottles, capsules, etc.
2. Description of the Related Art
Some foods, drinks, chemicals, etc., when brought into contact with oxygen in the air, are susceptible to putrefaction, denaturation or deterioration and as methods for preventing such, there have been hitherto practiced, for example, absorbtion and removal of oxygen in the air contained in sealed containers by incorporating deoxidants (reductive organic compounds such as sulfoxylates, dithionates, etc.), capable of absorbing oxygen, either put in a permeable container or wrapped with a permeable film, together with foods, drinks, chemicals etc. into the sealed containers, etc.
Further, for sealed containers such as beer cans, juice cans, food cans, etc., a method of replacing oxygen present in the air in a head space or dissolved in contents of the sealed containers with inert gases such as nitrogen gas, carbon dioxide gas, etc. has also conventionally been practiced. However, the method using deoxidants incorporated in the sealed containers directly or using permeable film wrapping encounters problems that as the deoxidants are contained together with the foods or drinks in sealed containers, they must be separated from the foods or drinks and that heat generated due to vigorous oxidation of the deoxidants can be removed only with difficulty, which may produce adverse effects on the contents, etc.; therefore the actual situation is that none of the above conventional methods has been practically used for storage of liquid food and drink as well as chemicals. Further, the method using inert gas has been found to be unsatisfactory for removing oxygen dissolved in the contents.
If sealed containers per se were prepared from materials having a deoxidation function, there would be no necessity of separately preparing deoxidants and handling would be simple and deoxidation of the afore said liquid materials would become easy and thus, a useful deoxidation method would be provided.
Through extensive investigations with an attempt to develop materials having a deoxidation function capable of achieving the aforesaid objects, the present inventors have found that by providing a hydrophilic coating layer on the surface of a metallic base material, deoxidation proceeds extremely rapidly without hindering oxidation of the base material and have arrived at the present invention.